Physical Pendulums

1. The problem statement, all variables and given/known data
"A circular hoop of radiusm 50 cm is hung on a narrow horizontal rod and allowed to swing in the plane of the hoop. What is the period of its oscillation, assuming that the amplitude is small?

2. Relevant equations

T= 2*pi(I/(MgD))^.5

3. The attempt at a solution

Ok... so if M is not given for the hoop and the rod, how do I go about figured it out? What is the value of D? And do I factor the moment of inertia for both the rod and hoop, and if so... how do I figure out the length of the rod, if it is not given.